Nov 17, 2011

Cells are the fundamental units of life. Whether they be unicellular or
multicellular life forms, all living organisms are composed of and
depend on cells to function normally. Scientists estimate that our
bodies contain anywhere from 75 to 100 trillion cells. Cells do
everything from providing structure and stability to providing energy
and a means of reproduction for an organism. The following facts
about cells will provide you with well known and perhaps little known
tidbits of information about cells.

1. Cells are too small to be seen without magnification.

Cells range in size from 1 to 100 micrometers. The study of cells, also called cell biology
would not have been possible without the invention of the microscope.
With the advance microscopes of today such as the Scanning Electron
Microscope and Transmission Electron Microscope, cell biologists are
able to obtain detailed images of the smallest of cell structures.

2. There are two primary types of cells.

Eukaryotic and prokaryotic cells are the two main types of cells. Eukaryotic cells are called so because they have a true nucleus. Animals, plants, fungi and protists are examples of organisms that are composed of eukaryotic cells. Prokaryotes include bacteria and archaeans.

3. Prokaryotic single-celled organisms were the earliest and most primitive forms of life on earth.
Prokaryotes can live in environments that would be deadly to most other
organisms. They are able to live and thrive in various extreme habitats.
Archaeans for example, live in areas such as hydrothermal vents, hot springs, swamps, wetlands, and even animal intestines.

4. There are more bacterial cells in the body than human cells.
Scientists have estimated that about 95% of all the cells in the body are bacteria. The vast majority of these microbes can be found within the digetive tract.

5. Cells contain genetic material.

Cells contain DNA
(deoxyribonucleic acid), the genetic information necessary for
directing cellular activities. DNA is a type of molecule known as a nucleic acid.
In prokaryotic cells, the single bacterial DNA molecule is not
separated from the rest of the cell but coiled up in a region of the cytoplasm
called the nucleoid region. In eukaryotic cells, DNA molecules are
located within the cell's nucleus. DNA and proteins are the major
components of chromosomes. Human cells contain 23 pairs of chromosomes
(for a total of 46). There are 22 pairs of autosomes (non-sex
chromosomes) and one pair of sex chromosomes. The X and Y sex
chromosomes determine gender.

Organelles have a wide range of responsibilities within a cell that
include everything from providing energy to producing hormones and
enzymes. Eukaryotic cells contain several types of organelles, while
prokaryotic cells contain a few organelles (ribosomes) and none that are
bound by a membrane. There are also differences between the kinds of
organelles found within different eukaryotic cell types. Plant cells for
example, contain structures such as a cell wall and chloroplasts that
are not found in animal cells. Other examples of organelles include:

Nucleus

Mitochondria

Endoplasmic Reticulum

Golgi Complex

Ribosomes

7. Different types of cells reproduce through different methods.
Most prokaryotic cells reproduce by a process called binary fission.
This is a type of cloning process in which two identical cells are
derived from a single cell. Eukaryotic organisms have a similar type of
reproductive method known as mitosis. Some eukaryotes also have the ability to reproduce sexually, which involves the fusion of sex cells or gametes. Gametes are produced by a process called meiosis.

8. Groups of similar cells form tissues.
Tissues are groups of cells with both a shared structure and function. Cells that make up animal tissues
are sometimes woven together with extracellular fibers and are
occasionally held together by a sticky substance that coats the cells.
Different types of tissues can also be arranged together to form organs.
Groups of organs can in turn form organ systems.

9. Cells have varying life spans.
Cells within the human body have different life spans based on the type
and function of the cell. They can live anywhere from a few days to a
year. Certain cells of the digestive tract live for only a few days,
while some immune system cells can live for up to six weeks. Pancreatic cells can live for as long as a year.

10. Cells commit suicide.

When a cell becomes damaged or undergoes some type of infection, it will self destruct by a process called apoptosis.
Apoptosis works to ensure proper development and to keep the body's
natural process of mitosis in check. A cell's inability to undergo
apoptosis can result in the development of cancer.